On the conflicting generic delineation in the Onopordum group (Compositae, Cardueae - Carduinae): a combined nuclear and plastid molecular approach

Abstract

The limits of the genera that compose the Onopordum group of the Cardueae–Carduinae are difficult to establish. There are two main life forms; one is exemplified in the genus Onopordum, which includes only biennial colonisers in the Mediterranean region and temperate Eurasia; the second life form is exemplified in the group of perennial herbs of the genera Alfredia, Ancathia, Lamyropappus, Olgaea, Synurus, Syreitschikovia and Xanthopappus, all of them growing in the mountains of central Asia. We explored relationships among the genera of the complex by using Bayesian and parsimony analyses of a combined dataset of nuclear and plastid DNA sequences. Our results confirmed that the group is natural and the two life forms correspond to well defined entities. Generic limits within the eight central Asian genera are, however, very difficult to establish. Our results suggested that the present genus circumscription is artificial, especially for the largest genus, Olgaea, which appears paraphyletic. Some solutions are suggested. The most preferable might be lumping all small genera together in a broadly redefined genus Alfredia, and assigning sectional rank to the natural groups that result from correlating morphology with our molecular results. However, none of the possible solutions is free of problems because morphological characters and molecular phylogeny are not fully congruent. Some considerations on the origin and peculiar adaptations for becoming a successful coloniser shown by Onopordum are also offered, finding parallels to these adaptations in other examples of biennial colonisers within subtribe Carduinae.